Present devices such as flashlights, for example, which are operated using energy storages (such as batteries, accumulators, and the like), always represent a trade-off between the (user's) objectives of maximum power output, for example brightness, and the longest possible operating period, for example burn time. For flashlights, for example, these objectives are generally taken into account by selecting a suitable luminous element having low consumption (for example, an LED light, etc.) and a suitable battery having the greatest possible capacity.
However, limits are imposed by objectives such as cost, weight, etc., which are no less important. As a result, for the above example either a maximum light output or a maximum burn time must be predetermined at the time of the design of the flashlight. The design is thus very inflexible with regard to various possible fields of application of the user. The burn time may be subsequently extended by the user only by purchasing another energy storage unit. However, not every activity for which the light is to be used requires the full light output, and in addition not every activity requires maximum burn time.
Similar problems of the inflexible design are also noted for other devices operated using an energy storage, for example battery-operated power tools, battery-operated gardening tools, electric vehicles, and the like.